Morris Minor Owners Club

Just wondering about something this morning...

I have an old, unopened Gallon jar of brake fluid that I was just about to throw away and it got me wondering. In THEORY water can leach in to just about anywhere to contaminate fluid, hence the short shelf life and even shorter service life. So, is the water actually bonding into the fluid or could it, in THEORY, be boiled off by cooking the fluid?

This is more of a "post Zombie apocalypse" question rather than a plan to save £5.

Any thoughts?

Brake fluid is hygroscopic, which means it absorbs water (like salt does) but I don't think it chemically combines with the water. So it might be possible to boil off the water, but I'd be concerned that this might degrade the brake fluid in some way. In any case, as water decreases the boiling point of brake fluid, I'd be worried that some of the brake fluid might boil off as well.
A knowledgeable chemist could provide you a definative answer, but I wouldn't try it - if you didn't poison yourself on brake fluid fumes, you might well die in the subsequent car crash caused by using the degraded brake fluid....

If the zombies are after you you won’t be wanting to use the brakes!

If it's 'only' heated to 100c surely only the water content will vapourise?

Alan

In theory, yes. But adding water will lower the boiling point of the brake fluid, although I don't know to what extent. Certainly brake fluid will boil when braking the car if there is too much water contamination in it. Not a good idea, safety-wise. So you'd want a laboratory to carry out empirical tests on it. Not something I'd like to try out in a saucepan in the kitchen!

As Rob says, spend a fiver on new stuff

Must admit when I rebuilt my braking system I was planning on using silicone but kept hearing negative things about it, but used it anyway! as I thought well it doesn't absorb moisture, is non corrosive on paintwork and it won't need flushing every couple of years.
Not had any problems with it, bled ok and not noticed it being compressible as some suggest.

Alan

I used silicone break fluid in my Spitfire for years. All was well. My new-to-me Morris Minor came wit Dot 4 so I am just waiting for a good time to switch. Dot 5 is much easier to keep in the car and on the shelf though a little more expensive. Hydroscopic materials are very difficult to separate completely by heating, as indicated the vapour, will always be contaminated with some of the higher boiling fraction and also in reverse. Much like ethanol and water - once 95% is achieved the alcohol wants to hang on to the remaining water. Producing absolute dry alcohol is difficult and costly.

When i rebuilt my moggy pickup in 1991 i fitted a complete new braking system. Having owned several vans in the preceding 10 years i was familiar with the routine of slave cylinders seizing up between mot's & it seemed i would have to replace one corner or the other every year. Iron cylinders with alloy pistons on the front & alloy cylinders with steel pistons on the back are a recipie for corrosion.
I filled the new braking system with Dot 5 silicone fluid. I could not tell any difference in feel on the brakes.
What i did notice was that the slave cylinders just kept working.
That truck was on the road for 17 years & i never replaced one. It sat on the driveway laid up for another 7 years & did not move. On uncovering it for its second restoration the brakes stilll worked & were not seized.
For me that says it all, with the price of replacement brake cylinders using the old type of fluid is false economy.

Hear hear from me, been using it for five years with the car standing for months in the winter and the brakes work every time.

Hmmm. I decided against silicone on the basis of the strongly worded advice from the manufacturer of the "Lockheed type" servo. On the basis of the reports here I rather wish I hadn't. Where I'm at is a 100% new braking system filled with DOT4, as yet unused, which I have to drain down to deal with a slight leak at the master cylinder. Has anyone used DOT5 with a cheapo servo, and would draining and replacing the fluid with DOT5 be possible without mixabilty issues?

There is so much conflicting info around dot 5 in theory all brakf components are supposed to be compatible, how well they adehere to this in china or wherever else the cheap servos are made is anyones guess.

I work on the principle that virtually every manufacturer still uses glycol fluid and there must be a good reason for this, most also specufy a 2 year change so I try to follow this.

I suspect the reason is, dot 4 is cheaper than silicone! I did hear that Rolls Royce use silicone fluid, can’t confirm that though. I have used it for a number of years and can’t report any issues.

If they use silicone fluid, they can't charge you for changing it every 2 years as per the service schedule.

They make more money from finance and servicing than from selling cars these days.